A fairly easy mile or so from the trailhead, Wahclella Falls offers a scenic hike and a huge roaring waterfall. Plus a cave and rocks to scramble over, though I didn't tell you that.
All year round.
Go east on I-84 to exit 40; take a right and the trailhead is right there at the end of the parking lot. [Google map].
This thing to do was suggested by
Best Hikes with Kids: Oregon – thank you!